It's a way to recharge, rejuvenate, and renew, says Page. "Anybody can benefit from a cleansing. The body is coming out of what might be called hibernation. It's a way you can jump-start your body for a more active life, a healthier life."

There's no vacuum or mop needed for this little "housekeeping" ritual. It means drinking juice -- a whole lot of juice and little else -- which pushes everything thing else out of your system, Page tells WebMD. You get the picture. You're clearing out all the tubes and pipes, as they say.

But to purists like Chris Strychacz, PhD, a research psychologist at the Naval Health Research Center in San Diego, Calif., fasting means "water only," he tells WebMD. He's been fasting for at least 25 years now, an annual weeklong ritual every spring.

"There's a big difference between fasting and dieting [as Page advocates]," Strychacz says. The effects on the body are quit different, he says.

Strychacz vividly remembers his first fast -- 17 days long. "It was extraordinary, a mystical experience. I felt like I'd figured out why Jesus and Plato and Socrates and Gandhi did it -- the clarity of thought, the peacefulness."

Fasting indeed has a long-standing spiritual tradition. "Almost every religion has some type of fasting ritual -- Lent, Ramadan, Yom Kippur ... the Hindus and Buddhists fast, too," says James Dillard, MD, assistant clinical professor at Columbia University College of Physicians and Surgeons in New York City. He's author of Alternative Medicinefor Dummies.

"There's definitely a spiritual factor," Dillard tells WebMD. But he's among the skeptics. "Whether [fasting diets] have any physiological benefit, I'm not so sure."

A study of anthropology gives plenty of evidence, Page says. In Chinese medicine, fasting is part of preventive health care. For many ancient cultures, fasting helped people "lighten up" after a long winter, shed the extra winter fat layer that provided warmth.